Protection of Ships Hulls against FoulingThe English expression fouling – the overgrowing of the hull – can be defined as the undesirable accumulation of microorganisms, plants, algae or animals on the wetted surfaces of the vessel’s hull. The most common are:
- The first stage of the bio fouling process starts at the moment the vessel has been immersed in seawater. Its surface immediately begins to accumulate adsorbed organic compounds as well as the molecules of polysaccharides, proteins and fragments of proteins.
- The second stage of fouling is the build-up of a biological microbe layer as the bacteria now has favourable conditions in which to propagate (micro fouling)
- The roughness of the microbe colonies helps to attract even larger organisms such as algae, marine fungi and mussels which present the third stage of fouling.
- In the fourth and the last stage of fouling (macro fouling) colonizers mainly consist of larger marine invertebrates (molluscs, sea moss, seaweed).
Why do we need anti-fouling coatings?The fouling of the vessel is the main reason for the increase in the roughness of the part of the vessel below sea level and therefore the increase in hull frictional resistance as it moves through water. As a result fuel consumption increases and vessel speed decreases. The slime (bio film – silt) on the submerged part of the vessel is responsible for an increase in vessel drag of approximately 2%. Seaweed increases the vessel drag by 10% and mussels by up to 40%. Increase in drag will directly impact on enhanced fuel consumption and significantly increased harmful gas emissions. The contemporary antifouling protection technology of the submerged part of the ship’s hull can be divided into two groups, which are BIOCIDE COATINGS AND ANTIFOULING COATINGS WITH ADDED NANO PARTICLES. BIOCIDE COATINGS function on the principle of biocide releasing. The main biocide compound is copper (Cu2O and Cu SCN) which has proven to be more efficient against bio fouling by animal organisms and less against fouling by plant organisms. The antifouling coating basically consists of a biocide agent and a fast degradable biocide agent accelerator. The most important features of the antifouling coating are: low solubility in sea water, its moderate price and it is also environmentally and human friendly. The antifouling coatings technology can be divided into:
- Natural Rosin-based Coatings
- Controlled Depletion Polymer Coatings, (CDP)
- Contact Leaching Antifouling Coatings
- Self-polishing Copolymer Coatings, (SPC)
- Hybrid Technology SPC/CDP Coatings